1. Field of the Invention
The present invention relates to an electroluminescence cell exhibiting high luminous efficiency and excellent durability.
2. Description of the Background Art
Use of organic materials as the positive hole transfer material and electron transfer material that constitute an electroluminescence cell has begun in recent years. Organic electroluminescence cells using such organic materials, hereinafter referred to as an "organic EL cell", are being vigorously researched. Organic materials that constitute such an organic EL cell are required to possess superior durability and high luminous efficiency.
Conventionally, as the organic material possessing a positive hole transfer capability, diamine derivatives which are low molecule organic materials such as aryl amine compounds such as N,N'-diphenyl-N,N'-di(3-methylphenyl)-4, 4'-diaminobiphenyl (hereinafter also referred to as "TPD"), and macromolecule organic materials such as polyvinyl carbazole are known.
However, the above-mentioned low molecular weight organic materials lack physical or thermal durability. A positive hole transfer layer based on such low molecular weight materials tends to deteriorate while the organic EL cell is in use or in storage.
On the other hand, macromolecule organic materials such as polyvinyl carbazole have a very high glass transition temperature (Tg) which provides a positive hole transfer layer with excellent durability. However, they present problems in actual application, requiring a very high driving voltage and yet yielding a low luminous efficiency due to a deficiency in positive hole transfer capability.
Meanwhile, although 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (hereinafter also referred to as "PBD") is known as an electron transfer material, thin films made of PBD lack stability.
In consideration of the above circumstances, an object of the present invention is to provide a block copolymer, which enables production of an organic EL cell having a high luminous efficiency and excellent durability.